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The fragile-X-related gene FXR1 is a human autoantigen processed during apoptosis
J Bolívar1, S Guelman, C Iglesias
1Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Cádiz, 11510 Puerto Real, Cádiz, Spain.
Abstract:
We describe a new human autoimmune antigen in a patient suffering from scleroderma with high levels of antibodies to nucleolus and cytoplasmic antigens. Using a Chinese hamster ovary cell expression library, we have shown that this antigen corresponds to the autosomal Fragile-X-related gene FXR1. The deduced amino acid sequence from the hamster cDNA is 97, 98, and 58% homologous to the human, mouse, and Xenopus laevis FXR1 genes, respectively. Expression of the hamster cDNA clone in Escherichia coli and antibody production indicates unequivocally the location of the FXR1 protein in the cytoplasm of hamster cells. Affinity chromatography followed by immunofluorescence microscopy analysis and immunoblots demonstrated the presence of autoimmune IgGs to FXR1 in the scleroderma patient. Immunolabeling studies in Jurkat cells, induced to apoptosis by anti-Fas/APO1 serum, indicated that the FXR1 antigens were clearly displaced from their original cytoplasmic location to several punctuated foci, resembling the bleb-like membranous structures characteristic of cells at certain stages of apoptosis. This phenomenon could be part of a putative mechanism in which the FXR1 protein is presented as a target for the autoimmune response in humans.
Insights
Researchers identified the Fragile-X-related gene 1 (FXR1) as a novel human autoimmune antigen in a scleroderma patient. FXR1 protein relocates during apoptosis, potentially becoming a target for autoimmune responses.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Scleroderma is an autoimmune disease characterized by autoantibodies to various cellular antigens.
- The specific antigens targeted in some scleroderma patients remain unidentified.
Purpose of the Study:
- To identify a novel human autoimmune antigen in a patient with scleroderma and high autoantibody levels.
- To investigate the cellular localization and behavior of the identified antigen during apoptosis.
Main Methods:
- Screening a Chinese hamster ovary cell expression library with patient serum.
- Cloning and expressing the identified gene (FXR1) in E. coli.
- Immunofluorescence microscopy, immunoblots, and affinity chromatography to detect autoantibodies.
- Immunolabeling studies on Jurkat cells undergoing apoptosis.
Main Results:
- The novel autoimmune antigen was identified as the Fragile-X-related gene 1 (FXR1).
- FXR1 protein is localized in the cytoplasm of hamster cells.
- Autoimmune IgGs against FXR1 were detected in the scleroderma patient's serum.
- FXR1 antigens translocated from the cytoplasm to punctuated foci during apoptosis.
Conclusions:
- FXR1 is a novel human autoimmune antigen associated with scleroderma.
- The relocation of FXR1 during apoptosis may expose it as a target for autoimmune responses.
- Understanding FXR1's role could offer insights into scleroderma pathogenesis.